This invention relates to a gel composition useful as a carrier for a composition to be dispersed, an adhesive composition incorporating the gel and to the method for preparing the gel.
Prior to the present invention, adhesive compositions have been known which are useful for forming an adhesive stick which generally takes the form of a relatively soft adhesive composition enclosed in a generally cylindrical housing. The adhesive composition can be progressively moved out of the housing to expose a portion thereof so that the exposed portion can be rubbed upon a suitable substrate to coat the substrate. The physical characteristics of the adhesive composition must be regulated so that excessive adhesive is not applied to the substrate during rubbing but while avoiding the need for excessive rubbing force which could cause the substrate to be damaged or ripped. The adhesive composition must also provide a relatively strong bond when dried and the bond so produced must be able to withstand normal atmospheric conditions over a relatively long period so that the bond can be maintained. The adhesive composition should provide a strong bond so that it is useful for bonding a wide variety of paper products such as paper sheets, photographs and cardboards. In addition, the adhesive composition should have a relatively long shelf life of about two years in that it should not crack when exposed to severe cold nor should it melt at temperatures below about 130.degree.F. Furthermore, the adhesive composition should provide a tear bond within a short period of time after application of within about twenty seconds.
An exemplary adhesive stick composition is disclosed by U.S. Pat. No. 3,576,776 to Muszik et al. This adhesive composition comprises a film-forming polymeric component and a gel comprising water or a mixture of water with an organic solvent and a water soluble salt of a long chain carboxylic acid. While this adhesive composition has been found to be somewhat satisfactory, the strength of the bond produced therewith is neither as strong nor as stable as would be desirable. In an important aspect, the adhesive compositions disclosed by this patent suffer the significant disadvantage that they are not remeltable. This places severe restrictions upon the processing conditions which can be employed in forming the adhesive compositions. Thus, for example, once the adhesive composition has been formulated it cannot be allowed to gel by virtue of cooling of the liquid portion of the composition since, in the gelled condition, it could not conveniently be placed into the housing for the adhesive stick.
Furthermore, the gel system disclosed in the Muszik patent must be prepared in a manner which is costly and which causes problems in maintaining a uniform composition throughout the gel preparation process. The Muszik gel must be maintained hot prior to adding the adhesive component in order to prevent premature gelling. This is undesirable since heating costs are high. Also, the liquid dispersant is being evaporated and condensed continuously during mixing which may cause liquid losses over the processing time required. It would be desirable to form the gel subsequent to dispersing the composition to be carried by the gel with a solution of one component of the gel so that the composition to be carried can be homogeneously dispersed therein. Furthermore, such a procedure would be desirable since heating requirements and evaporation losses would be minimized thereby.
Furthermore, it would be desirable to provide an adhesive composition which can be applied easily to a substrate, is temperature-stable and forms a strong bond. In a particular aspect, it would be highly desirable to provide an adhesive composition which is remeltable to facilitate processing to form an adhesive stick but which is capable of withstanding relatively high temperatures in the order of at least 130.degree.F.